Vascular epithelial growth factor (VEGF) plays a critical role in vessel growth and wound healing. Bevacizumab, a non specific VEGF inhibitor, has been successfully used for the treatment of eye diseases associated with neovascularization. The purpose of this randomized study is 1) to investigate the effects of intraoperative subtenon injection of bevacizumab on the outcomes of trabeculectomy surgery. 2) to measure plasma and aqueous levels of VEGF and assess its association with the outcomes of trabeculectomy surgery. Trabeculectomy surgery, where a small drainage canal is created at the front of the eye, is the most common glaucoma surgery performed worldwide. The goal of the surgery is to control intraocular pressure. Failure of this procedure is most commonly caused by excessive scarring of the surgical site. If scarring occurs, the drainage canal can close. By adding Bevacizumab at the time of surgery, wound healing may be slowed and surgical failure prevented.